As a machine to generate rotation power by external electric power, a general electric motor selectively and correspondingly includes any one of a field magnet and an armature to generate a rotation magnetic field or induced electricity between a stator and a rotor. The electric motor is generally and widely used in the whole industries needing power.
Electric motors are divided into DC motors and AC motors by kinds of electric power. The DC motors include a separately excited motor, a shunt-wound motor, a compound motor, and a series-wound motor. The AC motors include an induction motor, a synchronous motor, and a commutation motor.
Among the DC motors, a brushless DC (BLDC) motor has advantages including reduced noise and longer lifetime because it does not have a point of mechanical contact, unlike a conventional brush DC motor. Therefore, BLDC motors are widely used as electric motors for industrial machines, electric home products, transportation machines, and the like.
In the BLDC motor, a hole sensor is used as a position sensor of a rotor, to control a phase of current which is applied to stator winding, relative to a pole of the rotor which is a permanent magnet.